Many a pack of paper is not exactly white (5)
I believe the answer is:
cream
'not exactly white' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'many a pack of paper' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for r00).
'a pack of paper' becomes 'ream' (I can't explain this - if you can you should believe this answer much more).
'c'+'ream'='CREAM'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for cream that I've seen before include "Best - ointment" , "Top of milk or society" , "The best part -of the crop" , "Butterfat part of milk" , "Dairy product" .)